CN111259483B - Computing method for slope stability coefficient in cold region - Google Patents
Computing method for slope stability coefficient in cold region Download PDFInfo
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Abstract
The invention provides a method for calculating a cold region slope stability coefficient, which is characterized in that displacement and temperature of a cold region slope rock mass are measured through a temperature and displacement sensor, freezing and thawing depth of the cold region slope rock mass is obtained, a cold region slope rock mass freezing and thawing region and a rock mass of a cold region slope rock mass non-freezing and thawing region are layered, a method for calculating the cold and thawing slope stability coefficient based on a rock freezing and thawing damage creep model is established according to a freezing and thawing rock creep test, and sliding of the cold region slope freezing and thawing region is protected. The invention adopts the method for determining the cold region slope stability coefficient taking the freeze thawing characteristic and the creep characteristic into consideration by integrating monitoring the slope temperature, displacement and numerical calculation, and solves the problems of insufficient precision and the like of the traditional slope displacement monitoring method.
Description
Technical Field
The invention relates to the field of slope protection, in particular to a method for calculating a slope stability coefficient in a cold region.
Background
China is a plurality of sites with unstable side slopes, and under the influence of causes such as earthquake, heavy rainfall and the like, geologic disasters such as landslide, debris flow and the like often occur. Therefore, long-term monitoring and early warning of slopes near buildings such as highways, water conservancy facilities and residential areas are all important research contents of geotechnical engineering subjects. The most common method for monitoring the displacement of the traditional side slope is to monitor by adopting an inclinometer, a pressure gauge, a displacement gauge and other instruments, and the monitoring methods have poor precision and low automation and digitalization degrees. Moreover, the influence of the traditional cold region slope stability calculation method on the freezing and thawing time effect is not considered enough, and the simplified calculation result has a great difference from the actual result.
Disclosure of Invention
The invention provides a method for calculating a slope stability coefficient in a cold region so as to overcome the technical problems.
The invention provides a method for calculating a cold region slope stability coefficient, which is characterized in that displacement and temperature of a cold region slope rock mass are measured through a temperature and displacement sensor, freezing and thawing depth of the cold region slope rock mass is obtained, a cold region slope rock mass freezing and thawing region and a rock mass of a cold region slope rock mass non-freezing and thawing region are layered, a method for calculating the cold and thawing slope stability coefficient based on a rock freezing and thawing damage creep model is established according to a freezing and thawing rock creep test, and sliding of the cold region slope freezing and thawing region is protected.
Further, the method comprises the following steps:
s1: arranging a plurality of sensors on a cold region rock slope and arranging the sensors on the same straight line, wherein the straight line is parallel to the landslide direction of the cold region rock slope;
s2: according to the displacement and the temperature of the rock slope in the cold region measured by a plurality of sensors, determining a change curve of the rock stratum temperature along with the freeze thawing depth, and layering the rock mass in the freeze thawing region and the rock mass in the non-freeze thawing region by adopting the slope temperature gradient distribution characteristics;
s3: carrying out a rock creep test on a side slope freeze-thawing rock stratum and a non-freeze-thawing rock stratum, establishing a freeze-thawing creep damage model introducing a rock freeze-thawing damage factor, fitting test data through a least square method to obtain creep parameters of the rock at different freeze-thawing times, and then adopting the freeze-thawing damage creep model to calculate the stability coefficient of the freeze-thawing side slope at different freeze-thawing times;
s4: and setting a slope displacement warning alarm line according to the calculation of the freeze thawing slope stability coefficient, and sending out an alarm by the slope displacement warning system and adopting slope supporting measures when the set deformation value is exceeded.
Further, the sensor is an optical fiber Bragg grating inclinometer pipe, and an optical fiber grating temperature sensor and an optical fiber grating displacement sensor are arranged in the sensor; two longitudinal grooves are formed in symmetrical positions of the two sides of the outer wall of the fiber bragg grating inclinometer, the fiber bragg grating temperature sensor and the fiber bragg grating displacement sensor are stuck in the grooves, and the elastic modulus of an adhesive for sticking the fiber bragg grating temperature sensor and the fiber bragg grating displacement sensor after solidification is the same as that of the fiber bragg grating inclinometer.
Further, the calculation of the freeze-thawing slope stability coefficient adopts a strength folding method based on rock freeze-thawing damage and creep characteristics.
Further, the step S3 of calculating the stability coefficient of the freeze-thawing slope includes the following steps:
s31: determining the depth of a side slope freeze-thawing area according to a fiber grating temperature sensor;
s32: selecting a rock sample in a side slope freeze-thawing area and a non-freeze-thawing area to perform an indoor creep test;
s33: obtaining creep parameters before and after freeze thawing of a side slope rock sample, and providing a freeze thawing creep constitutive model based on rock thawing damage factors;
s34: establishing a freeze-thawing slope stability coefficient calculation model of the distribution characteristics of the freeze-thawing area and the non-freeze-thawing area;
s35: different rock parameters and constitutive models are given to the side slope freeze-thawing area and the non-freeze-thawing area;
s36: and analyzing the stability coefficient of the freeze-thawing slope by using a strength folding and subtracting method introducing the rock freeze-thawing damage factor and creep characteristic.
S37: and inputting creep time and freeze thawing times, setting a model displacement measuring point, gradually reducing the strength parameter, and carrying out numerical calculation.
At present, a traditional strength folding and subtracting method is often adopted in the slope stability calculation, and in the traditional strength folding and subtracting method, the mechanical property of a rock mass is represented by an elastoplastic constitutive model, and the whole slope is unstable by folding and subtracting the strength parameter of the rock mass. Compared with the traditional strength folding and subtracting method, the method reflects the freeze-thawing damage and creep characteristics of the rock mass due to the freeze-thawing influence and the time effect based on the rock freeze-thawing damage factor in the creep viscoelastic-plastic constitutive model, and uses whether the key point displacement of the side slope is stable after a certain time and whether the displacement is suddenly changed when the strength is reduced to a certain degree as a criterion of whether the side slope of the rock mass is unstable. Because the rock slope adopts the strength folding and subtracting method considering the freeze-thawing damage and creep characteristics, the influence of the rock freeze-thawing creep characteristics on the slope deformation and stability can be reflected.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments or the description of the prior art will be briefly described below, it will be obvious that the drawings in the following description are some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort to a person skilled in the art.
FIG. 1 is a flow chart of the calculation of the stability coefficient of the freeze-thawing slope;
FIG. 2 is a graph of a creep constitutive model based on a rock freeze-thaw damage factor according to the present invention;
FIG. 3 is a schematic diagram of a fiber Bragg grating inclinometer tube according to the present invention;
FIG. 4 is a top view of a fiber Bragg grating inclinometer tube according to the present invention;
FIG. 5 is a layout of a fiber Bragg grating inclinometer tube of the present invention;
FIG. 6 is a schematic diagram of the structure of the freeze thawing area and the non-freeze thawing area of the side slope according to the present invention;
FIG. 7 is a graph of rock creep obtained by a staged loading creep test in accordance with the present invention;
FIG. 8 is a schematic diagram of monitoring points determined by a conventional strength reduction method according to the present invention;
FIG. 9-1 is a graph of rock creep at the monitoring point for a strength reduction factor of 1.40 according to the present invention;
FIG. 9-2 is a graph of rock creep at the monitoring point for a strength reduction factor of 1.59 in accordance with the present invention;
FIG. 9-3 is a graph of rock creep at the monitoring point for a strength reduction factor of 1.60 according to the present invention;
FIG. 10 is a graph showing the displacement of the monitoring point in the X direction under different strength reduction coefficients according to the present invention;
FIG. 11-1 is a shear strain increment cloud image of a rock mass side slope at a freeze-thaw number of 0 according to the present invention;
FIG. 11-2 is a shear strain increment cloud chart of a rock mass side slope at a freeze thawing frequency of 10;
FIG. 11-3 is a shear strain increment cloud chart of a rock mass side slope at a freeze thawing frequency of 20;
FIGS. 11-4 are incremental clouds of shear strain for a rock mass side slope at 40 freeze thawing times in accordance with the present invention;
FIGS. 11-5 are incremental clouds of shear strain for a rock mass side slope at 80 freeze thawing times in accordance with the present invention;
FIG. 12 is a graph showing the relationship between the number of freeze thawing and the safety coefficient of a rock slope.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a method for calculating a stability coefficient of a side slope in a cold region, which is characterized in that a sensor is used for measuring the displacement and the temperature of the side slope in the cold region, rock mass above the boundary of the rock mass at 0 ℃ is taken as a boundary, rock mass above the boundary of the rock mass at 0 ℃ is taken as a freeze thawing region, rock mass below the boundary is taken as a non-freeze thawing region, the rock mass of the side slope freeze thawing region and the rock mass of the side slope non-freeze thawing region are layered, so that the freeze thawing depth of the side slope in the cold region is obtained, the numerical simulation of the stability of the side slope is combined, the rock mass of the side slope freeze thawing region and the rock mass of the side slope non-freeze thawing region is layered, different rock mass attributes are endowed along with the rock mass depth, a creep model based on a freeze thawing damage factor is adopted for calculating the stability coefficient (Fos) of the side slope by taking the strength and the creep damage of the rock mass as a critical value, the displacement of a corresponding measuring point when the numerical calculation reaches 1 (side slope critical sliding) is taken as a side slope displacement critical value, displacement monitoring data is obtained through a displacement sensor arranged at the actual side slope, and when the displacement critical value is exceeded, an alarm system gives an alarm, and a prompt measure is favorable for supporting the side slope.
FIG. 2 shows a creep constitutive model based on rock freeze-thaw damage factors according to the present invention, wherein the rock freeze-thaw damage factors are considered in each creep parameter.
As shown in fig. 1, the method comprises the following steps:
s1: arranging a plurality of sensors on a cold region rock slope and arranging the sensors on the same straight line, wherein the straight line is parallel to the landslide direction of the cold region rock slope;
s2: according to the displacement and the temperature of the rock slope in the cold region measured by a plurality of sensors, determining a change curve of the rock stratum temperature along with the freeze thawing depth, and layering the rock mass in the freeze thawing region and the rock mass in the non-freeze thawing region by adopting the slope temperature gradient distribution characteristics;
s3: carrying out a rock creep test on the side slope freeze-thawing rock stratum and the side slope non-freeze-thawing rock stratum to obtain a freeze-thawing rock creep damage model and parameters, and then carrying out calculation on the stability coefficient of the freeze-thawing side slope based on the rock freeze-thawing damage factor in the creep model;
s4: and (3) taking the displacement of the corresponding measuring point when the stability coefficient reaches 1 (slope critical sliding) as a slope displacement critical value through numerical calculation, obtaining displacement monitoring data through a displacement sensor arranged on the actual slope, and sending an alarm by an alarm system when the displacement monitoring data exceeds the displacement critical value, so that slope supporting measures can be taken in time.
And calculating the slope stability coefficient according to different freeze thawing times to obtain the condition that the stability coefficient is reduced along with the freeze thawing times. And (3) calculating the numerical value to obtain the displacement of the corresponding measuring point when the stability coefficient reaches 1 (slope critical sliding) as a slope displacement critical value. The displacement monitoring data are obtained through the displacement sensor arranged on the actual side slope, and when the displacement monitoring data exceed the displacement critical value, the alarm system gives an alarm, so that the side slope supporting measures can be taken in time. According to the invention, the predicted value obtained through numerical calculation is compared with the monitored value obtained through monitoring by the displacement sensor, and the slope stability coefficient is calculated by adopting the strength-fold-subtraction method of the creep damage model considering the freeze-thawing damage and creep characteristics, so that the problem that the influence of the freeze-thawing times and creep time on the slope stability coefficient is difficult to reflect in the general slope analysis is well solved, and the problem that the displacement critical value is difficult to determine is also solved.
The sensor is an optical fiber Bragg grating inclinometer pipe, and an optical fiber grating temperature sensor and an optical fiber grating displacement sensor are arranged in the sensor; two longitudinal grooves are formed in the symmetrical positions of the two sides of the outer wall of the fiber Bragg grating inclinometer 2, the fiber Bragg grating temperature sensor and the fiber Bragg grating displacement sensor are stuck in the grooves, the elastic modulus of an adhesive for sticking the fiber Bragg grating temperature sensor and the fiber Bragg grating displacement sensor after solidification is the same as the elastic modulus of the fiber Bragg grating inclinometer 2, and the deformation consistency of the fiber Bragg grating temperature sensor and the fiber Bragg grating displacement sensor and the inclinometer is ensured.
Specifically, fig. 1 is a flow chart of a slope stability calculation method based on an indoor freeze-thaw rock creep test and established by considering rock freeze-thaw damage and creep characteristics. As shown in fig. 3 and 4, the design and embedding of the fiber bragg grating inclinometer is schematic, the conventional inclinometer collects data by the portable vibrating wire inclinometer, the accuracy is poor, and the automation and digitization degree are low. The optical fiber Bragg grating is manufactured by utilizing the photosensitivity of the optical fiber, and the function of the optical fiber Bragg grating is equivalent to a filter. When light with a certain bandwidth is emitted to the fiber bragg grating, light with a specific wavelength is reflected back, and the rest of light continues to propagate forwards. Fiber grating sensors are sensitive to many physical quantities such as temperature, stress, strain, etc. When the physical quantity in the environment where the sensor is located changes, a change in the fiber grating and thus a change in the reflected wavelength is caused. The change of the physical quantity to be measured can be obtained through the change of the reflection wavelength. The fiber bragg grating temperature sensor, the fiber bragg grating displacement sensor and the inclinometer are integrated to form a fiber bragg grating inclinometer, the inclinometer is made of high-strength PVC inclinometer, each inclinometer is 2m long, 58mm in inner diameter, 70mm in outer diameter and 12mm in thickness, and the inclinometer is connected through a special connector. Two grooves are symmetrically arranged on two sides of the outer wall of the inclinometer pipe, the depth of the grooves is about 5mm, and the fiber bragg grating sensor is stuck in the grooves.
Further, the freeze-thawing slope stability coefficient calculation adopts a strength folding and subtracting method based on rock mass freeze-thawing damage and creep characteristics, and the specificity of the degree folding and subtracting method is that the influence of freeze-thawing times and creep time on the slope stability coefficient can be reflected; the strength folding and unfolding method based on the rock freezing and thawing damage and creep characteristics is characterized in that the rock freezing and thawing damage and creep characteristics are reflected based on the freezing and thawing damage factors in a creep model of the strength folding and unfolding method, so that the influence of seasonal temperature alternation, freezing and thawing damage caused by day and night alternation and creep deformation caused by dead weight action of a rock mass on a rock mass slope in a cold region is realized.
The traditional strength reduction method generally adopts three judgment bases: (1) the numerical calculation does not converge. (2) critical point displacement mutation. (3) having a plastic region therethrough. However, the strength folding method considering freeze thawing damage and creep characteristics is not suitable for the judgment basis in the conventional strength folding method. Because it is difficult to use the numerical convergence as the criterion of whether the slope is unstable or not when considering the creep property of the rock mass slope, the key point displacement is stable or not after a certain time and the displacement is suddenly changed or not when the strength is reduced to a certain degree can be used as the criterion of whether the rock mass slope is unstable or not.
Further, the freeze-thawing slope stability coefficient calculation comprises the following steps:
s31: determining the depth of a side slope freeze-thawing area according to a fiber grating temperature sensor;
s32: selecting a rock sample in a side slope freeze-thawing area and a non-freeze-thawing area to perform an indoor creep test;
s33: obtaining creep parameters before and after freeze thawing of a side slope rock sample, and providing a freeze thawing creep constitutive model based on rock thawing damage factors;
s34: establishing a freeze-thawing slope stability coefficient calculation model of the distribution characteristics of the freeze-thawing area and the non-freeze-thawing area;
s35: different rock parameters and constitutive models are given to the side slope freeze-thawing area and the non-freeze-thawing area;
s36: and analyzing the stability coefficient of the freeze-thawing slope by using a strength folding and subtracting method introducing the rock freeze-thawing damage factor and creep characteristic.
S37: and inputting creep time and freeze thawing times, setting a model displacement measuring point, gradually reducing the strength parameter, and carrying out numerical calculation.
The invention adopts a fiber bragg grating sensing system to perform freeze thawing slope stability coefficient, and mainly comprises a sensing network consisting of a light source, a sensor and an optical switch, a fiber bragg grating mediator, a server and a client with a remote monitoring function.
The light source in the fiber bragg grating sensing has wider bandwidth and stronger output power and stability, so as to meet the requirement of multi-point and multi-parameter measurement in a sensing system. The light source commonly used in the fiber grating sensing system at present mainly comprises SLED and ASE light source, and the output power is about 1-20mw.
Four optical fiber Bragg grating inclinometer pipes are arranged on the side slope, and direct measurement of physical quantities such as temperature, strain and the like is realized. The fiber grating wavelength is sensitive to temperature and strain at the same time, namely the temperature and the strain at the same time cause the fiber grating wavelength to move, so that the temperature and the strain cannot be distinguished by the fiber grating wavelength movement. Therefore, the temperature and strain response sensitivity coefficients of different fiber gratings can be determined to distinguish the temperature and the strain by an external temperature compensation ring or by utilizing two or two sections of fiber gratings with different temperature and strain response sensitivities to form a double-grating temperature and strain sensor.
Four monitoring points in different positions use optical cables and optical cable protection pipes which are connected through a single core to directly process transmission signals on an information processing and analyzing system based on a central monitoring room.
The fiber bragg grating sensing network analyzer is mainly used for data acquisition, signal processing, storage and the like; and then to a data processing and analysis system of the monitoring center through an optical fiber transmission system. In the system for monitoring the fiber bragg grating of the resistance body side slope of the hillside, demodulation of fiber bragg grating signals is the key of the system, and a portable high-resolution fiber bragg grating demodulator (precision + -5 pm, resolution 1 pm) is adopted, and mainly comprises two parts, namely a fiber bragg grating sensing detection signal processor, including information collection, processing, transmission and the like of the system, for completing conversion from optical signal wavelength information to electric signals, wherein analysis of central reflection wavelength of a sensor is the key of demodulation; the other part is electric signal processing (namely computer software) which comprises information processing, analysis, transmission, storage management, early warning and alarming functions, and the operation processing of the electric signal is completed.
The server mainly collects data from the fiber Bragg grating modulator through a specific command word, processes the data, displays the data in a graphic mode and a text mode, records changed Bragg wavelength, and completes connection with a plurality of clients to achieve data communication. The client primarily queries the server for wavelength information over a period of time.
As shown in fig. 5, in order to obtain the layout of the fiber Bragg grating inclinometer, drilling is performed in the slope rock stratum, then the sensor and the inclinometer are integrated to form the fiber Bragg grating inclinometer which is arranged inside, grouting protection is performed, so that the critical rock stratum depth of the cold region slope freeze thawing region is obtained, and then numerical simulation of slope stability is combined.
The invention adopts the fiber bragg grating sensor, and has the following advantages:
(1) Because the optical fiber has the characteristic of integrating sensing and transmission, the full-light on-line detection of the anchor cable can be well realized, the acquired data quantity is also distributed in the whole space, and various parameters (temperature, strain, pressure, displacement and the like) can be detected at the same time. Because in the determined slope engineering, the stress and the optical path signal attenuation are in a unique relationship. Therefore, after the attenuation of the light path is detected, the strain, the temperature and the position of the light path can be determined, and the light path has the characteristics of high sensing precision, high sensitivity and long service life.
(2) The anti-electromagnetic interference capability is strong. The water and electricity slope engineering has stronger electromagnetic field, has higher selection requirement on monitoring instruments, and the optical fiber sensor has extremely strong electromagnetic interference resistance, does not need shielding, grounding and lightning protection, avoids a part of lightning protection measures and reduces the cost.
(3) The system has good long-term stability. The monitoring system has the characteristics of good water resistance, corrosion resistance, high insulation, high pressure resistance, strong wavelength separation capability, insensitivity to environmental interference, unique temperature compensation technology and the like, and can achieve the effect of long-term stability.
(4) Has an intelligent development trend. The optical fiber detection information has small loss, and can realize long-distance communication and long-distance monitoring. After being connected with a computer network, the intelligent detection of self-detection and self-diagnosis can be realized.
FIG. 6 is a schematic structural diagram of a freeze-thawing region and a non-freeze-thawing region of a side slope, wherein rock masses of the freeze-thawing region and the non-freeze-thawing region are layered by adopting temperature gradient distribution characteristics of the side slope, and different rock mass attributes are endowed with the rock stratum depth to calculate the stability of the side slope, so that a sliding damage mode of a surface layer of the side slope can be well explained.
FIG. 1 is a flow chart showing the calculation of the freeze-thaw slope stability coefficient.
Step 1: firstly, according to the arrangement diagram of the fiber Bragg grating inclinometer pipes in the side slope shown in fig. 5, the inclinometer pipes are sequentially arranged on the inclined plane of the section view of the side slope from top to bottom, 5-10 sensors are installed on different depths of each inclinometer pipe, and then a plurality of temperature values of the side slope in different depths can be obtained. Finally, the depth of the freeze-thawing rock mass in the side slope can be determined through the temperature values of different depths.
Step 2: and (3) selecting rock from the side slope to prepare a standard sample, and then carrying out a creep test of the triaxial creep tester of the indoor rock.
Step 3: as shown in fig. 7, a rock creep curve is obtained by a graded loading rock creep test, and a rock freeze-thaw damage factor creep constitutive model capable of reflecting instantaneous elastic deformation, damping creep, constant velocity creep, plastic properties and acceleration segments is established as shown in fig. 2. From the test results, it is known that the creep properties of freeze-thaw rock are related to freeze-thaw times, stress states, and loading times. Based on the western original model, a creep constitutive model based on a rock freeze-thawing damage factor is provided, and strength reduction calculation is performed on the rock mass. The strength parameter, i.e. cohesion, of the rock mass material is based on the influence on the freeze-thaw damage factor of the rock. The strength of the rock mass is reduced by a method of gradually increasing a Strength Reduction Factor (SRF) through trial calculation after the strength of the rock mass is reduced until the rock mass reaches a critical damage state, wherein the critical damage state is a sign that a plastic region of a side slope is penetrated from a slope toe to a slope top and the force or displacement is not converged to serve as the instability of the side slope. At the moment, the corresponding strength reduction coefficient is the stability coefficient of the freeze-thawing slope based on the freeze-thawing damage and creep characteristics of the rock mass.
Step 4: and (3) establishing a calculation model of the freeze-thawing slope stability coefficients of different temperature gradient distribution characteristics according to the freeze-thawing area and the non-freeze-thawing area of the slope determined in the step (1).
Step 5: and (3) according to the rock creep parameters in the step (3), different rock creep parameters are given to the rock mass in different freeze thawing areas of the side slope.
Step 6: and (3) when the stability coefficient of the freeze-thawing slope is calculated, the same creep constitutive model is endowed to the rock mass in the freeze-thawing area and the non-freeze-thawing area of the slope, and the viscoplastic creep constitutive model which is established in the step (3) and takes the rock freeze-thawing damage factor into consideration is selected.
Step 7: before analyzing the stability coefficient of the freeze-thawing slope by adopting the intensity folding and subtracting method based on freeze-thawing damage and creep characteristics, analyzing the stability of the slope by adopting the traditional intensity folding and subtracting method, determining the sliding surface of the slope possibly unstable, and selecting 5 points on the sliding belt, as shown in figure 8. The effect of the rock creep properties on the slope deformation was observed by recording the change over time of the horizontal displacement at 5 points in the calculation of the strength folding and subtracting method taking the creep properties into account.
When creep characteristics are considered, the following criteria are selected to judge whether the slope reaches the limit damage state or not:
whether the displacement of the plurality of key points on the slide belt can be stabilized over a long period of time. Since the rock mass studied has creep-damping properties, for a stable slope, the deformation will always tend to stabilize to some point, although it progresses over time. If the strength of the rock mass is reduced to bring the slope to a limit, unrestricted plastic shear deformation of the slope along the runner is produced, which is much greater than the deformation produced by creep. At this time, the displacement of the rock mass on the side slope, especially above the sliding belt, is not stabilized after a period of time, so that some key points can be taken on the sliding belt, the change of the horizontal displacement of the points along with time is recorded, and if the displacement of the points cannot be stabilized for a long enough time, the instability of the side slope can be judged.
According to the rock creep curves of different freeze thawing times, a rock freeze thawing damage creep constitutive model which can reflect attenuation creep, constant-speed creep and acceleration creep can be built. According to the test results, the creep curve of the freeze-thawing rock is related to the freeze-thawing times, the stress state and the loading time. A creep constitutive model based on the rock freeze-thaw damage factor was then proposed, as shown in fig. 2.
The stress-strain relation expression in the creep constitutive model of the rock freeze-thawing damage factor is as follows:
(1) When sigma is<σ s In the time-course of which the first and second contact surfaces,
(2) When sigma is greater than or equal to sigma s In the time-course of which the first and second contact surfaces,
correction elastomer:
kelvin:
viscoplastomer:
wherein: epsilon is the total strain of the steel sheet,sigma is the load stress, E 0 E is the instantaneous modulus of elasticity in the elastomer 1 Elastic modulus, η, in Kelvin 1 Is the viscosity coefficient in Kelvin, eta 2 Is viscosity coefficient in viscoplastomer, D is rock freeze thawing damage factor, sigma s And the creep parameters of the rock under different freeze thawing times can be obtained by using the least square fitting test result for the rock yield stress and t for loading time.
Defining a rock freeze-thawing damage factor variable based on the elastic modulus, wherein the rock freeze-thawing damage factor D is expressed as follows:
D＝1-E n /E (6)
wherein: e is the initial elastic modulus of the rock when the rock is not frozen and thawed; e (E) n Is the elastic modulus of the rock at the non-freezing and thawing times.
The basic principle of the strength folding and subtracting method is that the shearing strength parameter of the rock mass is reduced in the elastoplastic numerical calculation of the rock mass, so that the slope reaches the critical damage state, and the stability coefficient of the freeze thawing slope is obtained. When the strength of the freeze thawing rock slope is reduced, the rock adopts Mohr-Coulomb (molar Coulomb) strength yield criterion:
c n ＝c(1-D) (8)
τ in n To the shear strength sigma of rock mass under different freezing and thawing times 0 C is the initial compressive strength of the rock mass n For the cohesion of the rock under different freeze thawing times, c is the initial cohesion of the unfrozen rock,
is the internal friction angle of the rock mass.
The strength folding method is to bond the strength parameter C of the material when the strength of the rock mass is folded n 、
At the same time divided by the same intensity reduction coefficient F s Lowering rock massThe trial calculation is carried out again after the intensity, and the intensity reduction coefficient F is gradually increased s The method of the method reduces the strength of the rock mass until the rock mass reaches a critical damage state, wherein the critical damage state is a sign that a plastic region of the side slope is penetrated from a slope toe to a slope top and the force or displacement is not converged to serve as the instability of the side slope. At this time, the corresponding intensity reduction coefficient F s The coefficient of stability of the freeze-thawing slope is obtained. The intensity reduction factor can be expressed as:
f in the formula s For the intensity reduction factor τ n To the shear strength sigma of rock mass under different freezing and thawing times 0 For initial compressive strength of rock mass, τ s Is the shear strength of the rock mass after being folded. The strength reduction process of the rock mass is as follows:
wherein, c n C, the cohesive force of the rock mass under different freezing and thawing times s For the cohesive force after the freeze thawing rock mass is reduced,
is the internal friction angle of the rock mass +.>
Is the internal friction angle after the rock mass is folded down. Therefore, the intensity reduction coefficient can also be expressed as:
the strength-folding method based on Mohr-Coulomb strength yield criterion carries out the strength-folding according to the method shown in the formula (10).
Before creep calculation is carried out on a slope engineering, the stability of the slope is analyzed by a traditional strength reduction method, and the sliding surface position and the short-term freeze-thawing slope stability coefficient in the critical failure state of the slope rock mass are determined. The calculation model is a molar coulomb model. The traditional strength folding and subtracting method is adopted, and the strength folding and subtracting coefficient is continuously corrected to repeatedly carry out trial calculation, so that the folding and subtracting coefficient when the slope reaches the critical damage state is finally obtained.
9-1 and 9-2, when the strength reduction coefficient takes a value of 1.40-1.59, the slope rock mass gradually enters into an attenuation creep stage after undergoing a short elastic deformation stage, the creep increment gradually decreases to zero, the creep curve is flat, and the deformation of the rock mass is macroscopically stable. 9-3, when the strength reduction coefficient takes a value of 1.60, after the creep time of 1 year (365 d) passes through the 5 monitoring points, the creep curve still does not reach a stable state, wherein the creep time can be set according to the time set during the actual slope stability evaluation, and is denoted by T; the freeze thawing time is determined by monitoring the rock mass temperature of the freeze thawing slope through a temperature sensor arranged on the actual slope, and T is used 0 A representation; the number of freeze thawing operations N of the slope is accordingly determined according to the time set for the actual slope stability factor calculation, i.e. n=t/T 0 . When the strength reduction coefficient is increased from 1.40 to 1.60, the total amount of deformation in the X direction corresponding to each monitoring point is shown in fig. 10.
As can be seen from fig. 10, the total amount of deformation corresponding to the monitoring points did not change significantly when the strength reduction coefficients were 1.40, 1.45 and 1.50. When the strength reduction coefficient is 1.60, the total deformation amount of the monitoring point in the X direction is obviously changed, and the total deformation amount is increased by 20 times when the relative strength reduction coefficient is 1.59. As the strength reduction coefficient increases, the total amount of deformation in the X direction also increases rapidly, and thus an inflection point appears in the graph of fig. 10. When the intensity reduction coefficient is larger than the inflection point value, the total amount of deformation in the X direction increases by 20 times or more. Through comprehensive analysis, considering the long-term stability of the rock-soil creep characteristic, the stability coefficient of the freeze-thawing slope is 1.59, and is reduced by 7.6 percent compared with the stability coefficient of the freeze-thawing slope obtained by the traditional strength reduction method, namely 1.72.
Compared with the change characteristics of the elastic-plastic displacement of the slope determined by the traditional strength reduction method, when the creep characteristic is considered, the displacement of the slope not only occurs on the surface layer of the slope body, but also has the tendency of gradually expanding towards the inside of the slope body, so that the slope is developed towards an unstable direction. Compared with the displacement of the elastic plastic deformation of the side slope, the displacement of the side slope is far larger than the elastic plastic analysis result under the creep condition, and the deformation of the side slope can be divided into an initial deformation stage and a uniform deformation stage. Therefore, the stability of the slope engineering should be evaluated with importance on the timeliness (i.e., creep characteristics) of the slope stability, and the influence of the freeze-thawing creep characteristics of the rock on the slope stability cannot be ignored.
FIG. 12 is a graph of incremental clouds of shear strain for a rock mass side slope at different freeze-thaw cycles. FIG. 12-1 is a cloud plot of rock mass slope shear strain for 0 freeze thawing times with a freeze thawing slope stability factor of 1.59. The maximum shear strain of the slope appears in the area near the slope surface above the slope toe of the slope, and no potential slip surface is formed, which shows that the rock mass slope stability before the freeze thawing cycle is better. As can be seen in FIG. 11-2, after 10 freeze-thaw cycles, the freeze-thaw slope stability coefficient dropped to 1.52. The increasing maximum shear strain area of the slope compared to fig. 11-1, while forming a potential slope slip plane, indicates a decrease in slope stability under the influence of freeze-thaw cycles. Fig. 11-3 are shear strain diagrams of a rock mass side slope after 20 freeze-thaw cycles, with a freeze-thaw slope stability factor of 1.45. The maximum shear strain area continues to increase and the slope potential slip plane continues to develop as compared to fig. 11-1, 11-2. FIGS. 11-4 are shear strain diagrams of a rock mass slope after 40 freeze-thaw cycles with a freeze-thaw slope stability factor of 1.38. The potential slip plane of the side slope expands to the upper left (the top of the slope) after developing into an arc. FIGS. 11-5 are shear strain diagrams of a side slope after 80 freeze-thaw cycles with a freeze-thaw slope stability factor of 1.15. In comparison with fig. 11-4, the potential slip plane of the side slope almost reaches the top of the slope, indicating that the potential slip trend of the side slope is a strip arc slip. 11-1-11-5, as the number of freezing and thawing times of the rock mass increases, the potential slip plane of the rock mass slope is continuously expanded to the top of the slope, and the maximum shear strain area is gradually increased, but the stability coefficient of the freezing and thawing slope is gradually reduced.
And performing parameter fitting on the rock mass freeze-thawing slope stability coefficient and the rock mass freeze-thawing times, wherein the relation is as follows:
F s ＝0.747×exp(-n/106.139)+0.840 (14)
wherein n is the number of freeze thawing times of rock mass, F s For the stability coefficient of the freeze thawing slope, the correlation coefficient R 2 The correlation coefficient is 0.997, and is an index for measuring the correlation degree between the stability coefficient of the rock mass freeze-thawing slope and the rock mass freeze-thawing times, and in general, the larger the correlation coefficient is, the higher the correlation degree is, and the value range of the correlation coefficient is 0<R 2 <1. The correlation coefficient in the invention is larger, which shows that the rock mass freeze-thawing slope stability coefficient has better fitting relation with the rock mass freeze-thawing times.
The relation curve of the rock mass freeze thawing times and the rock mass slope safety coefficient is shown in fig. 12, and the influence of the rock mass freeze thawing cycle times on the slope stability is larger. Along with the increase of the freeze thawing cycle times, the slope safety coefficient is gradually reduced, and finally the minimum value before the slope is destroyed is reached. The influence of damage and deterioration of rock mechanical properties on slope stability under the long-term freeze-thawing creep action is necessary to be considered in the support scheme selection and support structure design.
Step 8: and (3) taking protective measures on the surface layer freeze-thawing rock mass of the side slope in the cold region according to the stability coefficient of the freeze-thawing side slope obtained in the step (7).
It is calculated that the freeze-thaw creep effect results in a reduction of the freeze-thaw slope stability coefficient, since in slope engineering in cold areas, as the outside temperature alternates, the aqueous rock mass acts as a multiphase medium whose time-efficient deformation implies complex interactions of temperature fields, hydraulic fields and stress fields. On the one hand, seasonal and diurnal temperature alternating conditions lead to deterioration of rock damage. On the other hand, the freeze thawing rock mass generates volume expansion and frost heaving deformation. The creep deformation and frost heaving deformation of the rock mass are overlapped together, so that the deformation of the rock mass is gradually increased, and the instability of the side slope is caused. Therefore, necessary measures should be taken in the construction process, and the freeze thawing prevention materials are adopted to timely anchor the closed slope, so that the invasion of a large amount of precipitation or underground water is prevented, and the influence of the freeze thawing effect is effectively reduced.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (3)
1. The method is characterized by comprising the steps of measuring displacement and temperature of a cold region side slope rock mass through a temperature and displacement sensor, obtaining freezing and thawing depth of the cold region side slope rock mass, layering the cold region side slope rock mass freezing and thawing region and the rock mass of a cold region side slope rock mass non-freezing and thawing region, establishing a method for calculating the freeze-thawing side slope stability coefficient based on a rock freeze-thawing damage creep model according to a freeze-thawing rock creep test, and protecting sliding of the cold region side slope freezing and thawing region;
the method comprises the following steps:
s1: arranging a plurality of sensors on a cold region rock slope and arranging the sensors on the same straight line, wherein the straight line is parallel to the landslide direction of the cold region rock slope;
s2: according to the displacement and the temperature of the rock slope in the cold region measured by a plurality of sensors, determining a change curve of the rock stratum temperature along with the freeze thawing depth, and layering the rock mass in the freeze thawing region and the rock mass in the non-freeze thawing region by adopting the slope temperature gradient distribution characteristics;
s3: carrying out a rock creep test on a side slope freeze-thawing rock stratum and a non-freeze-thawing rock stratum, establishing a freeze-thawing creep damage model introducing a rock freeze-thawing damage factor, fitting test data through a least square method to obtain creep parameters of the rock at different freeze-thawing times, and then adopting the freeze-thawing damage creep model to calculate the stability coefficient of the freeze-thawing side slope at different freeze-thawing times;
the method for calculating the stability coefficient of the freeze-thawing slope comprises the following steps:
s31: determining the depth of a side slope freeze-thawing area according to a fiber grating temperature sensor;
s32: selecting a rock sample in a side slope freeze-thawing area and a non-freeze-thawing area to perform an indoor creep test;
s33: obtaining creep parameters before and after freeze thawing of a side slope rock sample, and providing a freeze thawing creep constitutive model based on rock thawing damage factors;
s34: establishing a freeze-thawing slope stability coefficient calculation model of the distribution characteristics of the freeze-thawing area and the non-freeze-thawing area;
s35: different rock parameters and constitutive models are given to the side slope freeze-thawing area and the non-freeze-thawing area;
s36: analyzing the stability coefficient of the freeze-thawing slope by using strength folding and subtracting method introducing the rock freeze-thawing damage factor and creep characteristic;
s37: inputting creep time and freeze thawing times, setting a model displacement measuring point, gradually reducing strength parameters, and carrying out numerical calculation;
s4: and setting a slope displacement warning alarm line according to the calculation of the freeze thawing slope stability coefficient, and sending out an alarm by the slope displacement warning system and adopting slope supporting measures when the set deformation value is exceeded.
2. The method of claim 1, wherein the sensor is a fiber bragg grating inclinometer tube, and a fiber bragg grating temperature sensor and a fiber bragg grating displacement sensor are built in the sensor; two longitudinal grooves are formed in symmetrical positions of the two sides of the outer wall of the fiber bragg grating inclinometer, the fiber bragg grating temperature sensor and the fiber bragg grating displacement sensor are stuck in the grooves, and the elastic modulus of an adhesive for sticking the fiber bragg grating temperature sensor and the fiber bragg grating displacement sensor after solidification is the same as that of the fiber bragg grating inclinometer.
3. The method of claim 1, wherein the freeze-thaw slope stability coefficient is calculated using a strength-fold-down method based on rock freeze-thaw damage and creep characteristics.
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